In the prior art, for a given solenoid configuration, one could modify the strength of the magnetic field by changing the current in the solenoid, however, the distribution and topology of the fields thus created remained essentially constant. A variant of the single solenoid often used, involves a number of independent solenoids wound on a single core, and adjacent to each other. Variations in magnetic field morphology can be achieved by the judicious choice of combinations of the solenoids powered and control of the current passing through each independent solenoid. This approach while feasible is cumbersome and with limited freedom of possible topologies. Furthermore, each desired configuration requires the physical implementation of a specific set of solenoids, thus strongly limiting the versatility of this method.
In my co-pending applications entitled "Electronic Modulation of Magnetic Fields" and "Switchable Superconducting Elements and Pixels Arrays", the general principles of using switchable superconducting elements to obtain modulation of magnetic fields in the vicinity of said elements was described. In yet another co-pending application entitled "Magnetic Flux Concentrators and Diffusers", we described how the magnetic field created between two poles of a magnet can be modified and controlled by introducing switchable superconducting elements of unique morphology. The present invention provides for the modulation of axial magnetic fields that are generated within solenoids. This is achieved by switching in and out of the superconducting state superconducting elements of a special design, specifically annuli that are concentric with the solenoid The result is a variety of configurations in which the normally axial magnetic field of a solenoid can be modulated temporally as well as spatially.
We believe these devices will find applications in the movement and position control of diamagnetic colloids (see my co-pending application entitled "Diamagnetic Colloids Containing Superconducting Particles"), particularly in unique drug delivery systems, new analytical instruments and magnetic separation systems.
The devices described may also find uses in a variety of diagnostic imaging systems, non destructive testing instruments and material characterization systems.
A variant of the devices described herein can be used as the magnetic field wiggler in a free electron laser (FEL) device. Unlike the current technology that requires the physical modification of the geometry of the fixed magnets in such wigglers, the present devices can provide for the electronic modification of the magnetic field configuration thus imparting an element of flexibility in FEL design heretofore not available.
As will be evident from the design of the present invention, the fact that the superconducting elements may have to be cooled to cryogenic temperatures does not prevent ambient operation of the usable space where the magnetic field is modulated. This, since the core containing the superconducting annuli responsible can be isolated thermally from the solenoid's hollow as well as from the solenoid's coil. While such cryogenic applications would be most cost effective in large industrial installations, where the cost of cryogenics installation is relatively small to the total cost of the system, smaller instrumentation with portable liquid nitrogen can employ the subject of this invention as well.